The present invention relates to an omni-directional wind turbine and more particularly to a vertical-axis turbine with expanded capability of converting wind power to electrical power.
The ever increasing global demand for electricity and the effect the generation of such has on the ecosystem, in concert with the lack of natural resources to keep up with growing demand, has provided new impetus to look toward the development of alternative and renewable energy sources.
Vertical-axis wind machines are well known in the art, as shown in U.S. Pat. No. 5,664,418xe2x80x94Walters and the patents cited therein, and have been the subject of numerous innovative proposals. Such wind machines have the inherent advantages of stability due to gyroscopic action of the rotor, simplicity of design due to the avoidance of yaw mechanisms and blade controls, and strength of construction. However, the fact that the sails of the rotor are exposed to the force of the wind during only one-half of each cycle and then must be shielded from the wind to prevent creation of back pressure during the remaining half of each cycle has been a major problem. A variety of structural changes have been proposed in an effort to avoid or minimize formation of back pressure on the sails during their return sweep, for instance: the segmented sails of Wilhelmxe2x80x94U.S. Pat. No. 5,004,878, the louvered sails of Darvishianxe2x80x94U.S. Pat. No. 4,015,911 and the reversal of a portion of the air stream of Baughmanxe2x80x94U.S. Pat. No. 4,350,900. But these, and similar, efforts have not been successful in overcoming the problems associated with the prior known vertical-axis wind machines. As a consequence, vertical-axis machines have not been commercially attractive and have not achieved substantial acceptance in competition with the horizontal-axis windmills.
The windmill construction which has been most commonly utilized for the generation of electricity is a plural-bladed propeller positioned vertically for rotation about a horizontal axis. This type of construction has been widely used because, when positioned into the wind, the entire surface of each blade of the propeller is exposed to the full force of the moving air. The commercial windmill industry has developed around the horizontal-axis construction and the aerodynamic principles and knowledge discovered in connection with atmospheric flight. Accordingly, it has become common practice to design such machines for the atmospheric/wind conditions of specific locations by varying the number and/or dimensions of the blades employed. The fewer the propeller blades, the more efficient the machines become at high wind speeds but the less efficient they are at lower wind speeds.
Because the blades of horizontal-axis windmills are coupled indirectly to an electric generator which is effective only at a constant design speed, and because the blades themselves become unsafe at high speeds, the horizontal-axis windmills have been capable of utilizing only a small percentage of the theoretically-available power in the wind. The multi-blade windmills have high starting torque at low wind speeds, harvesting up to 30% of the kinetic energy from the wind but become very inefficient at high wind speeds. The Dutch 4-blade machines, for instance, utilize only about 16% of the winds"" kinetic energy. The most common and efficient windmills today are of the two and three blade types designed for high tip speed operation. These machines harvest roughly 42% of the theoretical 59.2% kinetic energy from the wind. Such windmills operate within a narrow window or range of wind velocities defined by a cut-in wind speed of 3-5 mps (meters/sec.) and a cut-out wind speed of about 25 mps. To maintain a near constant level of torque to drive the generator has required either: complex controls, in the case of pitch control, or intricate blade designs, in the case of stall control, both of which are expensive to build and maintain. In addition, such wind machines require yaw mechanisms with motors, gearboxes, cable twist counters, etc. to keep the machine yawed against the wind. These requirements have combined to make the horizontal-axis windmills economically unattractive except in areas where alternative forms of electricity generation are not readily available.
Today""s windmill designs also have other drawbacks. They have problems with gyroscopic vibration when the machine veers with changing wind direction. They are vulnerable to high bending moments at the base or root of the blades as each blade passes by or into the wind-shade of the supporting mast as well as when being braked during tempest conditions. These bending moments lead to frequent blade replacements and high maintenance costs. Because of their massive structures, these machines, of necessity, are remotely located miles from the area of power usage, thus necessitating construction of expensive power grids to transport the energy produced to the point of consumption, (generally large cities). Consequently, an approximate eight to ten percent of the power generated never reaches its destination due to line and transformer losses. Lastly, because of opposition from environmentalists with regard to the esthetics in natural settings as well as prohibition from municipal regulating authorities due to safety hazards associated with these large-prop machines in populated areas, many areas which would be ideal for generating wind energy, such as atop large buildings, are simply off-limits due to opposing design constraints.
The present invention avoids the shortcomings of the prior known wind turbines by provision of a vertical-axis wind turbine which can be safely and efficiently operated over an expanded range of wind velocities.
The above object is realized by providing a vertical-axis wind turbine which includes a rotor/stator combination with provision for maximizing energy production by means of increasing wind velocity and pressure as well as eliminating back pressure. The rotor is connected in driving relation with a plurality of electrical generators which are capable of producing harmonic-free alternating or direct current and means for activating said generators in series or in parallel in accordance with a predetermined program.
The stator section of the present invention is constructed with upper and lower annular, conical sails joined by a series of arcuate deflection blades which circumscribe the turbine""s rotor at a predetermined angle. Since the kinetic energy of wind varies as a cube function, or third power, of its speed, the stator has been designed to utilize the law of conservation of angular momentum; effectively increasing the wind speed and kinetic energy at the rotor. Wind entering the vortical section of the stator is directed, concentrated and compressed to a higher velocity and energy level as it is focused cyclonically toward the airfoil blades of the rotor via the narrowing channels of the stator. As a result, at slow wind speeds the wind energy is increased and the envelope of operation of the turbine is widened, while at high wind speeds the flow across the stator blades will stall and create back pressure to be self limiting. The rotor blades feed upon this intensified wind energy, providing it with a much higher power output than can otherwise be obtained using a standard prio-art turbine per a given wind speed. Wind moving around the periphery of the stator will induce an area of significant low pressure on the concave side of all obstructive or wind-shade stator blades as a result of the venturi effect. This venturi (vacuum) not only eliminates back pressure on the return side of the rotor, but adds considerably to the overall torque. As the expended air exits the turbine it loses velocity as well as kinetic energy while it diffuses outwardly through the expanding vortical channels on the antipodal side of the stator so it merges smoothly with the air moving circumferentially around the turbine and moves smoothly and rapidly away.
The stator section of the turbine includes six vortical blades, distributed radially about the axis at sixty degree intervals and secured to upper and lower conical sails which circumscribe the upper and lower portions of the rotor. The conical sails are constructed with an external diameter essentially twice that of the rotor while the vortical stator blades are constructed with a radius fundamentally equal to the radius of the rotor and a chord length approximately 1.25 times its radius. The upper conical sail slopes vertically downward at substantially negative 20 degrees, with its inner vertices intersecting the horizontal vertices of the upper bearing support plate of the stator. Likewise, the lower conical sail slopes vertically upward substantially at a positive 20 degrees, with its inner vertices intersecting the horizontal vertices of the lower bearing support plate of the stator. Each stator blade curves helically inward toward the periphery of the rotor in a clockwise direction and the chord line of each stator blade is positioned at a negative 56 degree angle with respect to the axis when intended for operation in the southern hemisphere. For operation in the northern hemisphere the stator blades curve helically counterclockwise with the chord line of the blade being at a 56 degree angle with respect to the axis. Positioning the stator blades in such a manner allows the turbine to react to even the slightest localized winds as well as prevailing winds, all of which rotate counterclockwise north of the equator and clockwise south of the equator. This natural phenomenon acting upon the moving air mass, as well as the turbine rotor when in motion, is called the Coriolis effect and is caused by the rotation of the earth. The Coriolis effect is an example of the conservation of angular momentum. This bending force on a mass in motion is a very visible phenomenon. An object moving without any external force on it must move in such a way that its angular momentum remains constant. For example, if a spinning object moves closer to its axis of rotation its angular velocity must increase, as when a spinning skater""s arms are pulled closer to the body, increasing the rate of spin. Similarly, the motion of a wind blowing northward along the surface of the earth in the northern hemisphere reduces the distance of the air mass from the earth""s axis. Its angular velocity increases, forcing it to move eastward. Missile and satellite trajectories must also take into account the Coriolis effect produced by the rotation of the earth, river beds are dug deeper on one side, railroad tracks wear out faster on one side etc., depending on which hemisphere they are located in.
The rotor construction of the present invention is designed with a diameter approximately one-half the overall diameter of the stator and includes a plurality of concave or hemicyclic airfoil blades which are each constructed with a chord line equal to twice their radii and a chord length approximating one-third the overall diameter of the stator. The airfoil blades are firmly secured to, and sandwiched perpendicularly between, vertically dispersed circular plates on a vertical spindle to form separate stages or sections within the vertical rise of the rotor. Each stage comprises three airfoil blades which are positioned on radii of the plates at 120 degree intervals and attached adjacent the outer periphery of adjoining plates with their chord lines oriented perpendicular to the axis of rotation with the mid-section of the stage substantially open to the passage of air.
The rotor spindle is operatively connected to a plurality of transitionally-coupled generators, such as described in U.S. Pat. No. 6,020,725, for producing harmonic-free electrical power. The driving connection between the spindle and the individual generators is selectively engaged and disengaged mechanically as well as electrically under the control of a computer or programmable logic controller (PLC) in a predetermined arrangement and order to continually minimize the connected inertial load of the turbine and maximize electrical efficiency or power output.
The separate stages within the rotor smooth and eliminate output torque pulsations by transitionally optimizing the number of rotor blades in direct alignment or at their maximum angles of attack with respect to relative wind flow throughout the rotor and provide balance, strength, and stabilization to the entire rotor element.
Unlike the prior art vertical turbines, which produce torque at the expense of salient back pressure, each rotor airfoil of the present invention is sized to have a chord line dimension approximating one third of the rotor diameter. This unambiguously leaves the mid section of the rotor open to the flow of air around each hemicyclic airfoil blade and allows for a positive lift or torque for the full 360 degrees of rotation and eliminates static back pressure within each staged segment. This topological configuration maximizes the induced torque on the rotor at all angles of attack and is proven by applying Bernoulli""s equation to the air stream flowing around each of the airfoil blades. Those skilled in the art will understand that maximum pressure occurs within the concave or stagnation area of the airfoil blade where the air velocity equals zero
The present invention teaches away from standard art vertical and horizontal wind machines by providing: (1) A substantial increase in the internal rotor pressure and resultant kinetic energy provided by the two horizontal conical sails of the rotor together with the unique curvature and angle of the six vortical blades. This allows the present turbine to be installed in geographical areas heretofore considered to be inadequate as possible wind power sites due to the low average wind speeds; (2) A segmented or subdivided rotor which allows rapid air movement through each of its skewed subsections, providing a smooth output torque from each of the hemicyclic airfoil blades at all angles of attack for a full 360 degrees of rotation; (3) A further increase in the total torque applied to the rotor which results from the venturi effect or negative pressure created by circumferential air-flows around the vertical deflection blades of the stator, netting an unsurpassed torque for the full 360 degrees of rotation of the rotor; (4) Fabrication of stator blades with a left helix for locations in the northern hemisphere and a right helix for the southern hemisphere, which allows the present invention to take advantage of the earth""s Coriolis effect or force; and (5) A unique profile which permits installation in areas, such as atop tall buildings, where prior art turbines either cannot operate or cannot be installed due to structural design or safety concerns.